Effect of gradient of stress intensity factor at a crack tip on fatigue crack growth and correction method for the effect

Abstract

The stress intensity factor can be applied as an evaluation parameter of crack growth under small-scale yielding conditions. Moreover, the stress intensity factor corrected by the plastic zone correction can potentially be used as an evaluation parameter of crack growth for small-scale yielding criteria or beyond these criteria. In the previous study, the plastic zone correction method for that purpose was proposed. The method focuses on the gradient of the stress intensity factor at the crack tip, incorporating the term into the correction formula. To investigate the applicability of the correction experimentally, fatigue crack propagation tests were conducted in this study using three types of specimens with different gradients. The results show that the crack growth rate increased when the gradient was large although the effective stress intensity factor range was the same. This indicates that the gradient of the stress intensity factor at the crack tip affects the stress state in the vicinity of the crack tip and the crack growth rate increases as the gradient increases. When the correction of the stress intensity factor was applied, the crack growth rate could be evaluated independently from the gradient of the stress intensity factor. The correction is applicable around small-scale yielding criteria or beyond these criteria, but is not applicable under sufficiently large-scale yielding conditions.